One method to achieve filterless Class-D switching amplifier operation, increased efficiency, and reduced cost is to deliver current to the load only when needed, and once delivered, maintain the current without decaying or wasting energy in removing the current. This can be accomplished by using a ternary modulation scheme implemented in an H-bridge configuration having four states of operation as shown in FIG. 1, FIG. 2, FIG. 3 and FIG. 4 as disclosed in commonly assigned copending patent application entitled "Modulation Scheme for Filterless Switching Amplifiers", filed herewith, the teachings of which are incorporated herein by reference. Voltage and current waveforms are shown in FIG. 5 and FIG. 6 for analog input into the amplifier.
In the presence of an input signal, the waveforms change as shown in FIG. 6 in view of FIG. 5. The edges of the OUTP waveform 12 move away from each other, and the edges of the OUTN waveform 14 move towards each other. The voltage difference of these two signals 12 and 14, which appears across a load shown as L1, generate narrow pulses as shown at 15 of waveform 16. These pulses 15 also have the desired affect of doubling the single-ended PWM frequency. Current does decay as the speaker as a load and MOSFETS are lossy, as shown as waveform 18. If the polarity of the input signal is reversed, the edges of OUTN (14) move away from each other and the edges of OUTP (12) move towards each other.
There is desired a signal processing scheme for the signals just described above.